If you add first, it is 7×5{\displaystyle 7\times 5} and evaluates to 35.

If you multiply first, it is 3+20{\displaystyle 3+20} and evaluates to 23.

Is the first or second answer correct?

With no order of operations, both answers would be expected, but if an expression evaluates to more than one answer, math becomes ambiguous and does not work. For math to work there is only one order of operations to evaluate a mathematical expression.

The order of operations is Parenthesis, Exponents, Multiplication and Division (from left to right), Addition and Subtraction (from left to right). This can be remembered in two ways: "Please Excuse My Dear Aunt Sally" or PEMDAS.

Please note that for Multiplication and Division and Addition and Subtraction you do which ever one comes first going from left to right and that is why both PEMDAS and BODMAS work. The following list from top to bottom is the order of operations in Algebra. Operations at the top of the list are completed first, operations on the same line are completed from left to right.

Parenthesis ( )

Exponent ^

Multiply ×{\displaystyle \times }, Divide ÷{\displaystyle \div }

Add +{\displaystyle +}, Subtract −{\displaystyle -}

Parenthesis is a special operation that has the most precedence. You use the ( and ) signs to make a separate expression from a group of terms. You evaluate an expression in parenthesis first. You use parenthesis if you need to do an operation with less precedence first. If the term in Parenthesis is juxtaposed to a variable with no multiplication, then the variable and Parenthesis is ONE TERM. (example: 2x{\displaystyle 2x} is ONE TERM so if x=(1+2){\displaystyle x=(1+2)}, then 2(1+2){\displaystyle 2(1+2)} is ONE TERM and takes precedence in the Order of Operations)